[Thread Inquiry] Questions regarding R and F NPT connections
Thread Content
This post was last edited by luoshirong on 2024-1-5 at 22:42. My valve has R1/2 external threads, while the piping installed on-site by the user uses F NPT 1/2 internal threads. Can they be tightened together to create a seal? If so, how many turns can they be turned? Does anyone know? Since I wasn’t at the scene, I’d like to confirm now whether the product with R1/2 external threads can be used once it arrives at the customer’s location. I also know that these two thread standards are different; I’m looking for someone who understands thread standards and has practical work experience to ask for advice. I asked a worker in the processing field, and he said that 4-millimeter and 6-millimeter sizes are compatible, but larger sizes won’t work. I’m not sure if that’s correct
R1/2 refers to British imperial pipe threads, while NPT is American tapered pipe thread; the two are not compatible, so the threads on your small valve and those on the user’s piping cannot be connected directly. An adapter is needed for conversion, or one of the threads on the valve or pipe must be changed to match the other. .
R1/2 and NPT1/2 are standard and applicable; three turns or more is sufficient. See the pitch of these two standards
Theoretically, these two types of threads cannot be mated together. The thread profile angle of British imperial sealed pipe threads is 55°; both the thread crest and the thread root are arc-shaped, with a taper of 1:16. Reference planes are defined at the proximal end of the internal thread and in the middle section of the external thread. The taper of NPTF American pipe threads is also 1:16, but the thread angle is 60°, with both the thread crest and root being flattened. It can be said that these values are the same, or the error after tooth profile angle machining is not significant. Whether they can work together depends mainly on whether the pitch is the same. For sizes of 4 inches and 6 inches, both have 14 teeth per inch, while other pipe fittings have different numbers of teeth; therefore, only 4-inch and 6-inch pipes can be used together.
Firstly, the standards for the R1/2 and FNPT 1/2 threads are indeed different; the former is the British standard thread for pipes and fittings, while the latter is the unified American standard thread. Although both are 1/2 inch, they are not compatible due to differences in tooth shape and design. Regarding the question of whether they can be tightened, generally speaking, it is not possible to tighten them directly due to the different standards for these two types of threads. Forcing it in may cause damage to the threads or failure of the seal. As for the universal use of 4-point and 6-point types you mentioned, it mainly depends on the specific specifications and actual usage conditions. Generally speaking, smaller thread sizes may have a certain degree of versatility due to their fewer threads, but this versatility usually disappears at larger sizes. In summary, it is impossible to tighten them directly due to the different standards for the R1/2 and FNPT 1/2 threads. To ensure the proper use of the goods, it is recommended to communicate further with the user to confirm the thread standards on site, and provide threaded valves that meet those requirements. If necessary, alternative solutions can be provided or custom valves can be designed to meet the user’s requirements.
Chinese ZG, R (external thread); British BSPT, R (external thread), Rc (internal thread). ZG has now been replaced; R is being used instead. Fitters may not be aware of the difference between R and NPT. But experienced turners certainly know this, as there are several parameters that turners must pay attention to. Send a picture so we can compare.
The supply is provided according to the specified parameters; that’s all there is to it!
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